The present invention relates to an automatic focusing camera, and more particularly, to an automatic focusing camera provided with an automatic focus detecting device which includes measuring means for detecting an amount and direction of difference between an image forming position and a film surface and drives a taking lens to its focal point in response to an output of the measuring means.
In the past, an automatic focusing (hereinafter referred to as AF) system has been disclosed as an automatic focus detecting device for a camera in U.S. Pat. No. 4,508,443 of common assignment. This system includes an AF detector provided within a lens barrel for automating a focusing operation. With this arrangement, an AF control is achieved by an open-loop control when an amount of defocus is less than a threshold. Specifically, a taking lens is driven in the routine of &lt;MDRIV8&gt; shown in FIG. 22 of U.S. Pat. No. 4,508,443 to bring it into focus. In this case, since an address signal is produced by turning on and off an address switch on a lens range ring, the play in a lens drive system is practically negligible. However, the problem is only a play between the lens range ring and a lens focusing group. Such play is less than 1/100 mm calculated on a focus plane, so that it is negligible as to accuracy in AF. Consequently, in the routine &lt;MDRIV8&gt;, it is possible to obtain exact focusing accuracy without determining AF calculated values such as a CCD integration again by operating AF elements.
The AF system, however, which includes an automatic focus detection device within a lens barrel, requires as many devices as there are interchangeable lenses and lenses thus become bulky and expensive. Accordingly, these disadvantages can be eliminated when the AF system applies to a camera of the lens interchangeable type in which a drive source such as a motor is provided on a camera body and a driving force transmitting system and a lens driving mechanism are provided on an interchangeable lens barrel and these arrangements are connected by a coupler through a camera mount.
In this case, however, an integrated value in play occuring in the coupler and the like is nearly 1/100.about.15/100 mm calculated on the focus plane which is not negligible in accuracy of AF.